You're basically right. I'm not 100% sold on this idea, but I think it's a possibility. Most of what I'm seeing right now is CUE facing outward, e.g., to generate typed things from within nix. This[1] is a good example of that. Given how flexible CUE is, and given how similar nix is to HCL, I think it's possible to have CUE emit nix and provide some basic typing that way.

[1] https://github.com/jmgilman/nix-cue